We have disclosed in co-pending patent application Ser. No. 08/323,464, filed Oct. 14, 1994 now abandoned, a four-speed ratio transmission for use in an automotive vehicle having an internal combustion engine. That transmission is disclosed also in U.S. Pat. No. 4,966,050. The '464 application and the '050 patent are assigned to the assignee of the present invention.
The transmission disclosed in the '050 patent has four forward driving ratios. The torque flow paths for the transmission gearing are defined by a Simpson gearset and a simple planetary gearset, both gearsets being situated between the turbine of a torque converter and the torque output shaft. The Simpson gearset establishes three forward-driving torque ratios and the simple planetary gear unit, acting in cooperation with the Simpson gearset, establishes an additional ratio. A friction brake for the reaction element of the simple planetary gear unit is used to establish a torque reaction and an overrunning coupling establishes torque flow between two elements of the simple planetary gear unit.
A second overrunning coupling in the Simpson gearset establishes a non-synchronous ratio shift. Forward engagement is achieved by engaging a forward clutch during a shift from neutral to drive. A separate reverse engagement clutch is used to establish a torque flow path for reverse.
Ratio changes on upshifts as well as downshifts in the transmission gearing are controlled electronically to establish optimum shift quality.